WiMAX is defined as “Worldwide Interoperability for Microwave Access” by the WiMAX Forum, which was formed in April, 2001 to promote conformance and interoperability of the IEEE 802.16 standard. WiMAX is described as “a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL.”
One aspect of the standard provides a simple Point-to-Multi-Point (PMP) architecture. The PMP architecture includes a base station (BS) communicating over a single hop to one or more wireless mobile stations (MS). FIG. 1A shows an example of a PMP architecture in which BS 50 is in communication with MS 52 and MS 54. In an ideal case, conventional PMP transmission allows for a 50 km hop and transmission rates of approximately 30 Mbps in the direction from BS to MS and 17 Mbps in the direction from MS to BS. To provide suitable transmission over the single hop, a BS having a tall antenna with a good line of sight to the MS is typically required.
The current version of IEEE 802.16d also defines a mesh architecture. In a mesh network each node only transmits as far as an adjacent node. In a mesh network nodes can transmit data from nearby nodes to nodes that are too far away to reach in a single hop or do not have clear line of sight, resulting in a network that can span large distances. This introduces complexity to network control and resource scheduling. The current version of the IEEE 802.16d mesh network architecture is considered to be “connection-less”. Connection-less mode transmission is a transmission format in which packets are provided with header information sufficient to permit delivery of the packets without additional instructions.
The mesh mode as it is currently defined in the standard is not entirely compatible with the PMP mode due to different frame structures used for transmission of messages and data in each respective mode. The two modes also have different procedures for network entry. In addition, the mesh mode does not support handoff for mobility of the MS. The mesh mode also does not support OFDMA at PHY layer.